Measurement of swimming speed in sperm whales

Cetaceans spend their entire life in the water. Hence these animals represent important models for studying adaptations for aquatic environment. Although many scientists have been interested in how fast they can swim, accurate swimming speed measurements of free-ranging cetaceans are rare because it is difficult to observe them continuously. In particular, little is known about routine swimming speed of deep diver, such as sperm whales. To measure swimming speed of the sperm whales, we attached two-type suction-cup-attached tags including a data logger to sperm whales. One type was similar to that employed in several other studies (Type A). The other type was modified by us to get more precious velocity data (Type B). We attached the two-type tag to a total of 11 sperm whales (8 Type A and 3 Type B) and, obtained accurate swimming speed with 8 whales of them (5 Type A and 3 Type B). A total of 136 hours of accurate swimming speed data including 137 dives was obtained. Average velocity during the dive was 1.77 plusmn 0.39 m s-1 (n =137). Maximum velocity of each whale was 4.2-9.6 m s-1 (n = 8). In addition, we found the oscillations caused by the tail beat in the time-series velocity data, which was obtained by modified suction-cup-attached tags (Type B). The modified tags provide us routine and maximum swimming speed of the whales as well as the information of the tail beat.